Omeprazole and structurally similar sulfoxide compounds are known inhibitors of gastric acid secretion and are used as anti-ulcer agents. The sulfur atom of the sulfoxide group in asymmetrically substituted sulfoxides is chiral. Therefore, omeprazole and related sulfoxides exhibit optical isomerism at the sulfur atom of the sulfoxide. In fact, omeprazole exists as a pair of enantiomers; the S (−) enantiomer is referred to as esomeprazole.
Certain analytical and preparative methods for separation of the enantiomers of omeprazole are known in the art. For example, a reaction between a 6-methoxy analogue of omeprazole with R-mandelic acid in chloroform results in a diastereomeric mixture which may be separated by reverse phase chromatography. Preparation of a single enantiomer or an enantiomerically enriched omeprazole by asymmetric oxidation of a pro-chiral sulphide is also known. If a salt of the sulfoxide is desired, it may be obtained, for example, by a reaction with a corresponding alkaline or earth alkaline base.
Nevertheless, there is still a need for new processes of preparation of substantially optically pure or optically enriched isomers of sulfoxide compounds, as well as fore the resulting compounds, their salts, and their hydrates.